markdown preview: Allow toggling checkbox by click (#10364)

Release Notes:

- Added support for toggling a checkbox in markdown preview by clicking
on it (cmd+click)
([#5226](https://github.com/zed-industries/zed/issues/5226)).

---------

Co-authored-by: Remco Smits <62463826+RemcoSmitsDev@users.noreply.github.com>

crates/markdown_preview/src/markdown_elements.rs

@@ -58,7 +58,7 @@ pub struct ParsedMarkdownListItem {
 #[cfg_attr(test, derive(PartialEq))]
 pub enum ParsedMarkdownListItemType {
     Ordered(u64),
-    Task(bool),
+    Task(bool, Range<usize>),
     Unordered,
 }